← IGCSE Computer Science Paper 1

Encoding a word as 8-bit ASCII binary

Look up each letter's ASCII code and write it as an 8-bit binary group, then join the groups in order. Example: A = 65 = 01000001.

Part of: IGCSE Computer Science 0478 — 1.2 Text, Sound and Images — Module 7, ACARA Digital Technologies Years 7–8 — Representing Text, Images and Sound — Module 20

Understanding Encoding a word as 8-bit ASCII binary in IGCSE Computer Science Paper 1

What it does: The number of bits is the number of characters multiplied by 8. Each 8-bit group is converted to its denary ASCII code and then to a letter, giving the word HI. Every character gets its own group of 8 bits, so a word with 5 letters uses 5 groups. 65 = 64 + 1, so the bits are 01000001. 01000010 is 66, which is B. The groups must be joined in the same order as the letters. H comes first, so 01001000 comes first. 3 characters x 8 bits per character = 24 bits. Each 8-bit group is one character: 67 = C, 65 = A, 84 = T, so the message is CAT.

Common mistakes: Each character must be stored as a full 8-bit group. 0100010 has only 7 bits. B = 66 = 01000010. 01001000 is the binary for 72 (H), not 73. The ASCII code 73 for I is 01001001.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

🖨 Print worksheet + answer key Add Encoding a word as 8-bit ASCII binary to a class →

This module's key terms are also in a printable crossword (Modules 28–41) and word search (Modules 28–58).

Take this worksheet further — free with Cloodit

Each concept is reinforced from every angle — learned, then applied, then tested.

Learning
Duo
In 8-bit ASCII encoding, how is each character stored?
As a single bitAs one group of 8 bits
Matches
B = 66 = 1000010
↓
Only 7 bits are written. The group must be padded with a leading 0 to make 8 bits: 01000010.
Applying
Meanings
Term
8-bit ASCII encoding
Meaning
Look up each letter's ASCII code and write it as an 8-bit binary group, then join the groups in order. Example: A = 65 = 01000001.
Practice
C = 67 = 01000011
Testing
Gaps
A = 65 =
Check Answer
Spots
3A = 65 = 01000001
4B = 66 = 0100010

Cloodit turns curriculum-aligned coding content into journeys students work through one biome at a time.

The 'Constellation Wolf' badge — Space Legend, one of Cloodit's 106 collectible badges
Students earn collectable badges

Over 100 of them, across seven natural biomes.

Study Buddy
Students build a real study resource

Turns their work into revision material ready for Flash Cards and Exam study.

Diamond Dash — one of Cloodit's live, competitive Sprint games
Students lock in with Sprints

Live, competitive practice for the start of the lesson or a teacher-led lesson finisher.

A Cloodit certificate of achievement, ready to personalise and print
Custom printable certificates

Honour your top performers, or encourage a student who's trying hard — ready to print in seconds.

Add to class →

Quick Questions

1. In 8-bit ASCII encoding, how is each character stored?
A. As a single bit
B. As one group of 8 bits ✓
Every character gets its own group of 8 bits, so a word with 5 letters uses 5 groups.
2. Which is the 8-bit binary for A (ASCII code 65)?
A. 01000001 ✓
B. 01000010
65 = 64 + 1, so the bits are 01000001. 01000010 is 66, which is B.
3. Which is the correct 8-bit ASCII encoding of the word Hi (H = 72, i = 105)?
A. 01001000 01101001 ✓
B. 01101001 01001000
The groups must be joined in the same order as the letters. H comes first, so 01001000 comes first.
4. How many bits are needed to store the word CAT in 8-bit ASCII?
A. 24 bits ✓
B. 3 bits
3 characters x 8 bits per character = 24 bits.
5. What word does 01000010 01000001 decode to? (A = 65, B = 66)
A. AB
B. BA ✓
Decode each group in order. 01000010 = 66 = B, then 01000001 = 65 = A.

Match the Pairs

A = 65 = 01000001 → The letter A has ASCII code 65, which is written as the 8-bit binary group 01000001
01000011 01000001 01000010 → The word CAB stored as three 8-bit groups joined in the same order as the letters
Each character uses one group of 8 bits, so a 3-letter word needs 24 bits in total → 3 characters x 8 bits = 24 bits
To decode a binary message, split it into groups of 8 bits and look up each ASCII code → 01001000 = 72 = H, 01001001 = 73 = I
B = 66 = 1000010 → Only 7 bits are written. The group must be padded with a leading 0 to make 8 bits: 01000010.
CAB = 01000001 01000011 01000010 → The groups are in the wrong order. C must come first: 01000011 01000001 01000010.

Key Term

8-bit ASCII encoding
Look up each letter's ASCII code and write it as an 8-bit binary group, then join the groups in order. Example: A = 65 = 01000001.

Fill in the Blanks

1. A = 65 = 01000001
Hint: Type the 8-bit binary group for the code 65.
2. B = 66 = 01000010
Hint: Type the ASCII code number for B, the letter after A.
3. "CAT" = 3 x 8 = 24 bits
Hint: Type the total number of bits: 3 characters at 8 bits each.
4. 01000011 = 67 = C
Hint: Type the letter whose ASCII code is 67, counting on from A = 65.
5. "AB" = 01000001 01000010
Hint: Type the 8-bit group for the second letter, joined after the first group.

Spot the Error

Question 1
A word ← "CAB"
B C = 67 = 01000011
C A = 65 = 01000001
D B = 66 = 0100010
E join in order: C, A, B
Line D — Each character must be stored as a full 8-bit group. 0100010 has only 7 bits. B = 66 = 01000010.
Question 2
A word ← "HI"
B H = 72 = 01001000
C I = 73 = 01001000
D result ← 0100100001001001
Line C — 01001000 is the binary for 72 (H), not 73. The ASCII code 73 for I is 01001001.
Question 3
A bitsPerCharacter ← 7
B D = 68 = 01000100
C O = 79 = 01001111
D G = 71 = 01000111
Line A — Each character is stored as an 8-bit group, so bitsPerCharacter should be 8, not 7.
Question 4
A word ← "CAT"
B C = 66 = 01000011
C A = 65 = 01000001
D T = 84 = 01010100
Line B — The ASCII code for C is 67, not 66. 66 is the code for B. The correct line is C = 67 = 01000011.
Question 5
A bits ← 01001000 01001001
B 01001000 = 72 = H
C 01001001 = 73 = J
D message ← "HI"
Line C — ASCII code 73 is the letter I, not J. The correct line is 01001001 = 73 = I.

Student with a class code? Join your class →